1. Field of the Invention
This invention relates, generally, to the art of prosthetics. More particularly, it relates to a cushioned prosthetic liner that expands radially but not axially.
2. Description of the Prior Art
A residual limb, or residuum, expands and contracts throughout the day and over longer periods of time as well. Accordingly, a prosthetic liner should exhibit the quality of radial expandability to accommodate such changes in size.
Prosthetic liners are worn on residual limbs to cushion the contact area between the residual limb and a prosthetic socket. Most materials having utility as cushioning means are expandable in all directions. Thus, they expand radially to accommodate during-the-day changes, as well as long-term changes, in the volume of the residual limb. Such expandability is desirable, but these liners also expand axially (longitudinally) as the patient walks. Such axial expansion is undesirable because it causes "milking" of the residual limb. The adverse effects of milking are well-known to prosthetists.
U.S. Pat. No. 4,923,474 to Klasson et al., which is incorporated hereinto by reference, relates to a cushioned prosthetic liner having a generally tubular construction and a rounded, closed distal end. In a first embodiment, Klasson et al. disclose the idea of a prosthetic liner made of a material that exhibits radial elasticity and limited longitudinal elasticity. In a second embodiment, the distal end of a prosthetic liner is if formed of an embedment material that is freely expandable in a radial and a longitudinal direction. The disclosure of the second embodiment includes a suggestion that a wire is added to the embedment material to reduce stretching in the longitudinal direction. How slipping of the wire relative to the embedment material could be prevented is untaught.
In a commercial embodiment of the Klasson et al. prosthetic liner, a fabric is laminated onto a silicone prosthetic liner to achieve the claimed properties. The fabric is of the woven, open mesh type and adequately performs its intended function. However, the fabric has the same shape as the liner, i.e., it is essentially tubular with a closed end. The fabric is laminated into the distal end of the liner, and extends roughly one-third to one-half of the longitudinal extent of the liner. The radial expandability is limited by the fact that the material completely encircles or covers the distal end of the prosthetic liner. Such a structure inherently includes substantial resistance to radial expansion.
If the wire of the second embodiment, discussed above, includes multiple wires that encircle the longitudinal axis of the prosthetic liner, those wires would present substantial resistance to radial expansion. If a single wire is used, its inherent rigidity would also present substantial resistance to radial expansion.
Significantly, the fabric stretches in the longitudinal direction and milking of the residuum results. If a wire material that somehow did not slip relative to the embedment material were substituted for the fabric, the longitudinal stretching would be overcome, but the quality of radial expandability would be diminished as aforesaid.
Prosthetic liners are typically about fourteen or so inches in length. In most cases, a few inches are trimmed from the open proximal end to accommodate bending of the patient's knee. The Klasson et al. material that provides radial expandability while inhibiting longitudinal stretching is restricted to the distal third or distal half of the liner. If it were to extend further toward the proximal, open end of the liner, it would not stretch in the anterior region when the knee is bent. There would be insufficient expandability when the knee is flexed because the embedment material would completely surround the knee.
To better appreciate why the Klasson et al. device remains subject to at least some milking action, it should be understood that the restriction of the material that permits radial expandability while resisting longitudinal stretching to the distal one-half or one-third of the liner and the elasticity of the embedment material reduces the amount of surface area over which the weight of the prosthesis may be suspended. For example, the weight of a ten pound prosthesis suspended at the end of the Klasson et al. device is spread over the two square inch area of the distal attachment plate and not over the entire inner surface of the prosthetic liner, resulting in a negative pressure of five pounds per square inch during the swing phase of the wearer's gait. This results in the milking process.
An improved cushioned prosthetic liner is needed that would spread the weight over a greater surface area to reduce the milking action.
U.S. Pat. No. 5,830,237 to Kania, which is incorporated hereinto by reference, discloses a cushioned prosthetic liner formed of a fabric where one side thereof is coated with a gel. However, the fabric is stretchable in all directions, including radial and longitudinal. Thus, the Kania structure does not perform the anti-milking function for which the Klasson et al. structure is designed.
Accordingly, there remains a need for a cushioned prosthetic liner that is expandable in a radial direction yet substantially nonexpandable in a longitudinal direction. The needed prosthetic liner should not include inherent limitations to radial expandability.
More particularly, there is a need for a prosthetic liner that exhibits substantially the same ideal properties as proposed in the Klasson et al. disclosure, but which does not include a wire or a fabric liner that only covers the lower third or lower half of the liner.
There remains a need as well for a structure that limits milking to a substantially greater degree. The improved means for preventing longitudinal stretching and allowing radial expansion should extend the entire length or substantially the entire length of the prosthetic liner without adversely affecting flexing of the knee. The improved means should include materials that are easily cuttable with ordinary scissors so that the prosthetic liner could be cut to size as needed. The materials used should not present an abrading edge when cut.
Moreover, there is a need for a cushioned prosthetic liner that spreads the suspended weight of the prosthesis over a larger surface area to reduce the effects of milking.
However, it was not obvious to those of ordinary skill in this art how the needed improvements could be provided, in view of the art considered as a whole at the time the present invention was made.